Electrochromic materials capable of changing the optical properties thereof by applying a voltage are known in the related art. As a product using an electrochromic material, a smart window which may adjust the amount of light transmitted by switching between a colored state and a decolored state is known.
Those products using a material that may modulate the transmission spectrum for near-infrared rays are also called smart windows. Since most of the infrared rays from the sun are near-infrared rays, controlling the transmission spectrum for near-infrared rays is almost equal to controlling the acquisition rate of solar heat due to sunlight. In addition, such a smart window may also prevent infrared rays from going outdoors from a room in winter. The wavelength of the infrared rays radiated from the room is about 10 μm, which is classified as far-infrared rays. Accordingly, it is possible to obtain an ideal state in which the heat of the room does not escape as radiant heat by the smart window given the characteristics of reflecting far-infrared rays. In this case, even when the transmission spectrum is controlled so that near-infrared rays do not enter in summer, it is possible to maintain characteristics of reflecting far-infrared rays. Therefore, it is possible to obtain an ideal state in which near-infrared rays and far-infrared rays are prevented from being incident from the outside.
PTL 1 and PTL2 disclose an electrochromic device and an electrochromic nanocomposite thin film capable of shifting the resonance frequency of localized surface plasmon resonance (LSPR) as a means for changing optical properties. PTL 3 discloses an electrochromic device having a nanostructure used in PTL 1 and PTL 2. In addition, NPL 1 discloses individual characteristics of various nanocrystals that may be used as an electrochromic material.